Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
  • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
  • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
  • G11B7/0945—Methods for initialising servos, start-up sequences
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
  • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
  • G11B7/094—Methods and circuits for servo offset compensation
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
  • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
  • G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
  • G11B7/13925—Means for controlling the beam wavefront, e.g. for correction of aberration active, e.g. controlled by electrical or mechanical means
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
  • G11B2007/0006—Recording, reproducing or erasing systems characterised by the structure or type of the carrier adapted for scanning different types of carrier, e.g. CD & DVD

Definitions

• the present invention relates to compensating for deviations in light spot quality on optical discs, and more particularly to compensating for spherical aberrations caused by using numerical apertures that are les than optimum.
• Optical discs use light of a predetermined wavelength from a laser diode read and write information to and from an optical disc. Light reflected from the optical disc is used to control focusing, tracking and laser power characteristics. A problem that can occur in the light beam focused on the disc is that the amount of spherical aberration of the spot is too large for optimal recording. Spherical aberration can be caused by various reasons including: mismatches between the objective lens design and the actual cover layer thickness of the disc. The mismatch can be cancelled by adapting the properties of the optics resulting in an optimal spot for recording.
• Blu-ray optical systems include a spherical aberration (SA) compensation servo to correct for spherical aberrations.
• SA spherical aberration
• the SA-servo can be implemented with collimating optics, or LC-cell, or telescope optics.
• BD Blu-ray Discs
• SA spherical aberration
• Spherical aberrations occur more predominantly in optical disc systems that have shorter focal lengths and higher numerical apertures. Spherical aberrations can also result from various layers in optical discs.
• a new standard in optical discs is the Blu-ray standard that employs a large numerical aperture, short focal length and multiple recording layers.
• the Blu-ray standard provides highly desirable features such as extremely high density recording. It is also very desirable that Blu-ray readers and writers be capable of using older standards such as CDs and DVD.
• optical drives employ technologies that use numerous wavelengths to accommodate different types of optical discs that will be used with an optical drive. Each of these different wavelengths will, typically, employ a different numerical aperture (NA).
• NA numerical aperture
• Embodiments provided herein address the above discussed shortcoming in the prior art by providing spherical aberration (SA) adjustment.
• SA spherical aberration
• the SA adjustment provided is particularly useful for writing to CDs, but these embodiments are also useful for DVDs.
• a CD/DVD system that reads and writes with SA correction is provided. Measurements used for SA correction are taken in terms of measured jitter during reading.
• Fig. 1 is a schematic diagram of a multiple light optical reader/writer system
• Fig. 2 is an illustration of jitter vs. spherical aberration at average speeds
• Fig. 3 is an illustration of jitter vs. spherical aberration at high speeds.
• Spherical aberration (SA) correction is provided for CD writing in a double (CD + DVD), triple (CD + DVD + BD) or quadruple (CD + DVD + BD + HD-DVD) writer, which use the same light path for CD and DVD.
• Fig 1 is a schematic view of optical system 10 of the type used within in a BD- drive that employs a moving collimator lens (collimator) 14.
• Fig. 1 is illustrative of the type of optical system 10 employed within the drives used to read and record a Blu-ray disc 12. It should be understood that the system 10 shown in Fig. 1 is an illustration of an embodiment but that other embodiments are also envisioned. For example, these are no HD-DVD laser illustrated in Fig. 1, but embodiments using the HD-DVD are clearly envisioned. In a Blu-ray system as illustrated in Fig. Ia, a 450 nm light emanates from Fig. Ia.
• Blu-ray laser 16 which has a substantial portion reflected from beam splitter 26 through collimator lens 14.
• the collimator lens 14 takes the light incident from the beam splitter 26 and forms parallel light that is incident upon mirror 24.
• Mirror 24 reflects the parallel light towards objective lens 18; which focuses the light beam upon disc 12.
• Light reflected from disc 12 is formed into parallel light by objective lens 18.
• the focal position of objective lens 18 is controlled by focus offset servo 19.
• Light reflected from the disc passes through objective lens 18 and is reflected by mirror 24 through collimator lens 14.
• the reflected lightbeam that passes through collimator lens 14 converges towards beam splitter 26 which passes a substantial portion to servo lens 22 and onto detector 22. Still referring to Fig.
• additional lasers 15, 17 emit light of a different wavelength than Blu-ray laser 16 and also have has a substantial portion reflected from beam splitters 25, 27, respectively through collimator lens 14.
• the additional lasers 15, 17 emit light of a wavelength for infra-red and red that are used for CDs and DVDs, respectively.
• the placement of additional lasers 15, 17 as shown in Fig. 1 is only an example.
• the configuration in Fig. 1 is used as an example for the purpose of discussing the embodiments disclosed herein.
• the collimator lens 14 takes the light incident from beam splitters 25, 27 and forms parallel light that is incident upon mirror 24.
• Mirror 24 reflects the parallel light towards objective lens 18; which focuses the light beam upon disc 12.
• Light reflected from disc 12 is formed into parallel light by objective lens 18.
• the focal position of objective lens 18 is controlled by focus offset servo 19.
• Light reflected from the disc passes through objective lens 18 and is reflected by mirror 24 through collimator lens 14.
• the reflected light beam that passes through collimator lens 14 converges towards beam splitters 25, 27 which pass a substantial portion to servo lens 22 and onto detector 22.
• the spot on the disc can be defocused by actuating focus offset servo 19 which move the objective lens 18 relative to the disc in the direction indicated by arrow 19.
• Changing the position of the collimator lens 14 by collimator servo 15 can make the light beam diverge or converge, as desired, creating at least a partially, non-parallel beam.
• This non-parallel beam generates additional spherical aberration in the objective lens. This adds to the spherical aberration generated by the mismatch between the objective lens 18 and the cover layer thickness of the disc.
• the BD drive shown in Fig. 1 employ conventional 4-segment photo-diode detector elements are commonly used for focus-error and radial tracking-error signal generation. More complicated photo diode detector elements to measure the spherical aberration would result in an increase in costs to the system. While, it is envisioned that other photo diode detector elements can be used, this discussion herein employ conventional 4-segment detector elements without using additional detectors.
• the focus offset and SA- servo can be optimized using the jitter of the read HF-signal.
• blank recordable discs like BD-R, rewritable BD-RE or DVD+R, no data is available from which to generate the HF-signal. Therefore, a factory pre-set value or a value that is determined using a similar type of disc (CD or DVD) is used for initial optimization values for the focus offset and SA- servo during start-up within blank recordable and rewritable optical discs.
• CDs and DVDs because CDs normally do not have serious sensitivity issues for SA and DVDs are designed to tolerate the errors in SA within the DVD specification.
• no SA correction mechanism exists in conventional CD/DVD reading and writing systems. Therefore, no measurement for SA exists and no SA correction takes place. The closest mechanism currently existing to the measurement of SA in such systems would be jitter determination, and the resulting sensitivity would be so low that no reliable correction could be carried out.
• SA correction systems do exist (such as for BD) and the sensitivity of CD and DVD to the SA correction is high enough to allow for reliable optimization via jitter as a suitable quality function.
• the sensitivity of writing is such that optimizing SA leads to an improved writing performance with higher margins.
• the optimum SA correction adjustment is found by measuring jitter during the reading back of test writing in the factory. It has been found that the optimum value for reading corresponds to the optimum value for writing (as one would expect). Hence, on the basis of a read back optimization; the optimum SA for writing is created. Accordingly, this process delivers a basic optimum value that can be used for all discs of a given type (e.g. CD value for CD-R/RW).
• Figures 2 and 3 illustrate examples of measuring jitter various amounts of spherical aberration. In Fig. 2, jitter is provided as a function of spherical aberration for average speeds in a system of, or similar to, that illustrated in Fig. 1. In Fig. 2, jitter is provided as a function of spherical aberration for high speeds in a system of, or similar to, that illustrated in Fig. 1.
• the optimum SA correction adjustment is found by measuring jitter during read back in the drive itself at start-up and/or Optimum Power Calculation (OPC). This delivers an accurate correction for a disc that is matched to the given drive.
• OPC Optimum Power Calculation
• the system employs a mechanism such as a conventional SA correction actuator using known methodologies.
• the system in compatible with CD/DVD R/RW types of optical discs.
• These CD/DVD R/RW types of optical discs have varying substrate thicknesses. These variations in the thickness of substrates effectively create varying SA aberrations that affect the effective writing power.
• the discs with the largest thickness variations across the disc create the largest amount in variations in SA aberrations.
• the read performance of the discs and in particular jitter in determined.
• the SA correction actuator is adjusted so that the jitter during reading is within a predetermined range. This range would be in the vicinity of the lowest jitter.
• the optimum values for SA correction are those values having the lowest amount of jitter.
• the system adjusts the SA correction actuator to the same predetermined range that was determined during reading for the lowest amount of jitter.
• the same SA correction determined during reading by observing the jitter is used for writing.
• the drive signals to the SA correction actuator will have a signal before or during writing that changes the actuator setting.
• the signal would generally be in the form of a on the SA actuator during start-up or OPC procedures.
• a CD/DVD disc is placed in the drive, and the speed has been set. Initially, the disc is checked for any written data. This occurs in disc start-up.
• the factory SA correction value is applied. If it is desired to find a more accurate value of SA for the actual writing (e.g. in the above case of an unwritten disc), then the optimum power control (OPC) can be performed using the setting found or used after start-up. Then the SA correction measurement process is repeated on the part of the OPC where test -data at optimum power was written. This will yield an optimum value for SA correction that can be used for that disc on that drive.
• OPC optimum power control
• Another embodiment provides for improved writing across the disc could by applying varying SA correction values during calibration management breaks.
• the varying SA correction values will yield very good optimized results.
• This strategy could be different for CD and DVD type discs, as calibration management in CD implies a seamless link which is not as robust as DVD linking (part of the standard). Additionally, DVD sensitivities are higher, particularly DL (dual layer) with spacer variations; therefore, there is sufficient reason to apply it for DVD.
• the foregoing embodiments can be employed to optical writing systems and high speed writing systems.
• the foregoing embodiments can be used individually or in combination for optical writing systems that use CDs, DVDs, BD and HD-DVDs writing systems.
• Infra-red is the color used by CDs, Red is used by DVDs, Blue is used by Blu-ray Discs BD and red is also used by HD-DVDs).
• optical writing systems including, but not limited to: double writers that use either blue or red with infra-red; triple writers that use blue, red and infra-red; or quadruple writers that use blue, with red (for DVD and HD-DVD) and infra-red.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Head (AREA)
• Optical Recording Or Reproduction (AREA)

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• 2007
  • 2007-07-24 US US12/377,150 patent/US7936646B2/en not_active Expired - Fee Related
  • 2007-07-24 CN CNA2007800303464A patent/CN101506880A/zh active Pending
  • 2007-07-24 EP EP07805227A patent/EP2070086A1/en not_active Withdrawn
  • 2007-07-24 JP JP2009524262A patent/JP2010500701A/ja active Pending
  • 2007-07-24 WO PCT/IB2007/052944 patent/WO2008020354A1/en active Application Filing
  • 2007-07-24 KR KR1020097005042A patent/KR20090045935A/ko not_active Application Discontinuation
  • 2007-08-10 TW TW096129761A patent/TW200818171A/zh unknown

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